NMA E-Newsletter #204: Proper Speed Zoning—Standard vs. Reality

Executive Director of the NMA Foundation Jim Walker recently sent us an interesting document chock full of common-sense information on speed zoning. Jim described it as “one of the clearest manuals about how to set proper speed limits. If this manual were followed precisely, speed traps would be almost non-existent.”


Indeed, we reviewed it and thought it could have been one of Jim Baxter’s long-lost musings. Let’s take a look at some of the wisdom contained therein.


“Any alteration and posting of speed limits on municipal or county streets and roads… must be based on an engineering and traffic investigation that determines such a change is reasonable…Altered speed limits established solely on the basis of opinion are considered contrary to the intent of the statute.”


“Research has shown that higher traveling speeds are not necessarily associated with an increased risk of being involved in a crash. When drivers travel at the same speed in the same direction, even at high speeds, as on interstates, they are not passing one another and cannot collide as long as they maintain the same travelling speed. Conversely, when drivers travel at different rates of speed, the frequency of crashes increases, especially crashes involving more than one vehicle. The key factor is speed variance. The greater the speed variance or the distribution of speeds the greater the number of interactions among vehicles. Thus, drivers attempting passing maneuvers due to speed variance increase the risk of having collisions.”


“Drivers tend to pay less attention to speed limit signs, which they consider unreasonable unless there is an inordinate degree of enforcement. On the other hand, unreasonably low posted speed limits are commonly violated by drivers essentially making enforcement difficult and operating speeds higher than what would exist with proper realistic posted speed limits.”


“Generally, a higher number of crashes occur when the speed differential is greatest. Individual speeds at the 85th percentile level are by definition the safest speed for travel.”


“Most drivers on a road segment select a reasonably safe speed based on their conscious and subconscious reaction to many factors as previously mentioned. By obtaining a true measure or profile of the observed range of speeds, a realistic speed can be determined in terms of providing a posted speed limit beyond which enforcement can be applied.”


“Uniform traffic control devices do not bring uniform traffic control unless uniform enforcement and uniform traffic laws and ordinances are perceived to be reasonable when applied to these devices and to driver performance.”


“The primary purpose of speed zoning is not intended to be a revenue producing program, contrary to the belief of some drivers and, unfortunately, to a few local jurisdictions.”


“For speed limits to be of traffic safety value, they must be realistic and acceptable to most drivers…Use of unrealistically low speed limits usually results in high violation rates and large variance in speed, which negates speed zoning.”


Would you be surprised to learn these sage words actually come from a manual published by the Florida Department of Transportation (FDOT) titled “Speed Zoning for Highways Roads and Streets in Florida“?


It’s a worthy attempt to provide education about proper speed zoning practices, but we must wonder about the effectiveness of the implementation. Florida consistently ranks at, or near, the top of the NMA’s annual speed trap rankings, and the state is home to such notorious speed trap towns as Lawtey and Waldo.


This scenario plays out in other states as well. In Michigan, for example, the state police vigorously promote the safety benefits of proper speed zoning. The state even enacted a law (Public Act 85) to compel municipalities to set speed limits based on the 85th percentile formula. Yet, many Michigan communities still rank at the top of our speed trap listings.


We know that Michigan’s campaign represents a sincere desire to enhance public safety and encourage reasonable traffic enforcement. We assume FDOT has the same goals in mind.


But the reality is that municipalities across the country continue to operate abusive and illegal speed traps, despite the efforts of enlightened agencies like the Michigan State Police. A huge gap exists between what enforcement policies get adopted at the state level and what actually takes place at the local level. Until this changes, communities will continue to ignore established traffic engineering practice, common sense, state law and the safety needs of motorists.

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